1. Field of the Invention
The present invention relates to a linear motion rolling guide unit that linearly guides a movable element to be moved in a linear motion mechanism such as a machine tool or industrial robot.
2. Description of the Prior Art
A typical example of this type of linear motion rolling guide unit of the prior art is shown in FIG. 1.
As shown in the drawing, this linear motion rolling guide unit has track rail 2, in which track surfaces 1 are formed along the lengthwise direction, and a slider in the form of sliding unit 5 able to move relative to track rail 2, and having rolling element circulating path 4, which contains load bearing track grooves 4a corresponding to track surfaces 1 and return paths 4b parallel with said load bearing track grooves 4a. A plurality of rolling elements in the form of balls 6 are arranged and contained within said rolling element circulating path 4, which bear the load by circulating while rolling over track surfaces 1.
More specifically, the above-mentioned sliding unit 6 has casing 7, in which the above-mentioned load bearing a track grooves 4a and return paths 4b are formed, and end caps 8 and 9 fastened to both the front and back ends of said casing 7. Furthermore, direction changing paths 8a, which connect the above-mentioned load bearing track grooves 4a and return paths 4b and serve to change the direction of balls 6, are formed in said end caps 8 and 9 (the direction changing path formed in end cap 9 is not shown).
The linear motion rolling guide device having the constitution described above is, for example, arranged on the bed of a machine tool (not shown), and track rail 2 is fastened to said bed with bolts. A table for supporting workpieces and so forth is then bolted to sliding unit 5, with this operating as the movable side.
The linear motion rolling guide unit having the above-mentioned constitution is normally used by applying preliminary pressure by a device not shown to the balls 6 that roll over the load bearing region to prevent sliding unit 5 from rattling. As a result, said linear motion rolling guide unit of the prior art had the disadvantage of sliding unit 5 slightly oscillating in all directions in the manner of demonstrating a so-called weaving phenomenon when balls 6 either entered the load bearing region or left the load bearing region.
In addition, in guide units having a relatively long sliding distance, it is extremely difficult to obtain a highly precise degree of parallelism during travel at low cost.
Therefore, in order to solve these problems, a linear motion rolling guide unit is proposed like that shown in FIGS. 2 and 3. The same reference numerals are used for those constituent members that are either identical or correspond to the constituent members of the linear motion rolling guide unit shown in FIG. 1.
As shown in the drawings, in this linear motion rolling guide unit, sliding unit 5 has, for example, four casings 7 arranged in a row in the lengthwise direction of track rail 2, end caps 8 and 9 arranged on both ends, coupling members 15 provided to extend along the sides of each of said casings 7, and bolts 16 that fasten said coupling members 15 to each of casings 7, with the overall structure being formed to have a long shape. Furthermore, as shown in FIG. 3, load bearing track grooves 4a and return paths 4b are formed in each casing 7.
According to the linear motion rolling guide unit described above, by coupling a plurality of casings 7 in a row to compose a long sliding unit 5, stability can be improved by increasing the number of balls 6. Consequently, in addition to it being possible to prevent weaving of sliding unit 5, it is also possible to achieve a highly precise degree of parallelism during travel at low cost. In addition, the rated load is also increased.
Despite this, in the above-mentioned linear motion rolling guide unit, although the number of casings 7 must be increased in order to increase the rated load, since the length of each casing 7 in terms of a component are formed equally, said linear motion rolling guide unit has the disadvantage of it being difficult to suitably set the total length of sliding unit 5 to match a machine tool and so forth in which said linear motion rolling guide unit is to be incorporated.
In addition, in the above-mentioned linear motion rolling guide unit, since there is the possibility of the load bearing track grooves shifting out of position at the joints of each casing 7, said linear motion rolling guide unit has the additional disadvantage of increased sliding resistance due to the circulation of balls 6 not being smooth in such case.
In addition, as the length of the load bearing track grooves becomes longer, aggregation and dispersion phenomena occur at locations where balls 6 are subjected to an unbalanced load of the load bearing track grooves when an unbalanced load is applied to sliding unit 5, thus resulting in an increase in sliding resistance.